The present invention relates to an optical disk recording apparatus which forms a visible image on a disk surface of an optical disk, such as a CR-R/RW, a DVD+R/RW, or a DVD-R/RW, by use of a laser, and a method of forming the visible image on the optical disk.
Recording a visible image, such as characters or graphics, on a recording surface of an optical disk or a label surface (a surface opposite the recording surface) of the same by use of a laser has been known.
For instance, Patent Document 1 proposes a technique of providing a visible light characteristic changing layer at a position which is viewable from a label surface side of an optical disk; and exposing the visible light characteristic changing layer to a laser beam to thus change a visible light characteristic of the layer and render a visible image.
Patent Document 2 proposes a technique of using a reversible phase change material for a recording film of an optical disk, which enables recording of a visible image by use of a laser, and rewriting recorded graphics.
Patent Document 3 proposes a technique of newly writing a visible image on a recording surface of an optical disk on which a visible image has already been recorded.
Patent Document 1: JP-A-2002-203321
Patent Document 2: JP-A-2003-016649
Patent Document 3: JP-A-2004-039019
Patent Document 3 describes a technique of utilizing an FG pulse signal representing the rotational frequency of a spindle motor when a visible image is recorded on a disk surface of an optical disk, and taking as a reference pulse an FG pulse which is acquired at a timing when a specific address has been detected, and detecting a position radiated by a laser beam while taking the reference pulse as a reference.
When the optical disk on which the visible image has been rendered is taken out of the recording apparatus and the optical disk is again set to render a visible image, control is performed such that the number of FG pulses acquired during one revolution of the optical disk is increased so that positioning can be performed with high accuracy (Paragraph 0073 in Patent Document 3).
However, when an angle is detected while the FG pulse is taken as a reference, an error in detection of an angle becomes greater. For instance, when eight FG pulses are output per one revolution of the spindle, a maximum error in detection of an angle is 360/8=45 [deg.].
Moreover, in order to diminish the error in detection of an angle, the number of FG pulses per revolution of the spindle must be increased as mentioned above. However, an increase in the number of FG pulses usually results in a cost hike.